1. Field of the Invention
The present invention generally relates to systems for reducing the initial force required to actuate a valve from the fully closed position. More specifically, the present invention is directed to a system to provide easier actuation of high pressure rotary valves, e.g., my HEMIWEDGE.TM. valve described in U.S. Pat. No. 4,962.911 incorporated by reference herein.
2. Description of the Background
It is well known that the force required to initially open or completely close a valve is much greater than the force required to increase or decrease the opening of an already opened valve. When frilly closed, in addition to friction between contact surfaces of the valve seat and valve element, the initial opening force must overcome the pressure differential across the valve. Once the valve has been opened, adjustment of the valve is much easier because neither the friction nor pressure differential is present.
In high pressure pipelines, the operating force required to initially open a valve is substantially more than the force required to alter the valve opening. With hand operated valves employing an operating lever, this greater initial force may be applied by extending the length of the operating lever. In simple operations, this may be accomplished by using a longer operating lever or by placing a cheater pipe over the operating lever to extend its length. However, the use of long operating levers or cheater pipes may not be practical in many situations. For example, this solution may be unacceptable in confined or close quarters. Nor is it generally applicable where the operating lever comprises a circular handle. Nor is it generally applicable where the valve is operated by an electrical, pneumatic, hydraulic or other automatic actuator. Because much less force is required for later valve adjustment, the size of automatic actuators has been determined by the initial opening force required. Therefore, it has been necessary to employ an automatic actuator much larger than would have been required for most operations of the valve.
The development and introduction of the HEMIWEDGE.TM. valve has greatly exacerbated this problem. The HEMIWEDGE.TM. valve and a driver therefore are described and claimed in my U.S. Pat. Nos. 4,962,911 and 5,333,834, both of which are incorporated by reference herein. Because of its compact design, the HEMIWEDGE.TM. valve is particularly adaptable for use in high pressure pipelines in restricted access areas. Accordingly, the problem of producing the greater force required to initially actuate a rotary valve from its fully closed position became more apparent with use of the HEMIWEDGE.TM. valve. An improved actuator system was required which was capable of developing the greater force required to initially open the HEMIWEDGE.TM. and other rotary valves using a conventional, manual or automatic actuator.
There has been a long felt but unfulfilled need in the industry for an efficient means for reducing the force required to initially operate a valve by increasing the force which must be applied during the initial opening of the valve. The present invention solves that need.